In general, as self-emitters of light for use in display devices, there are field emission elements and electroluminescence (EL) elements. Among them, the EL elements are divided into an organic EL element using an organic material as a light emitting layer, and an inorganic EL element using an inorganic material as a light emitting layer.
The organic EL element comprises an anode, a cathode, and an organic EL layer of a very thin film that is sandwiched between the electrodes of two kinds, i.e. the anode and the cathode, and made of an organic light-emitting compound. When a voltage is applied between the anode and the cathode, holes from the anode and electrons from the cathode are respectively injected into the organic EL layer and recombined, and molecules of the organic light-emitting compound forming the organic EL layer are excited due to energy produced thereupon. In the course of deactivation of the molecules thus excited toward the ground state, a luminous phenomenon is generated. The organic EL element is a light emitter utilizing this luminous phenomenon.
The organic EL layer has a single-layer structure or a multilayer stacked structure including at least one of an organic layer called a light emitting layer that emits light by recombination of holes and electrons, an organic layer called a hole transport layer that is liable to be injected with holes and reluctant to move electrons, and an organic layer called an electron transport layer that is liable to be injected with electrons and reluctant to move holes.
In recent years, the organic EL elements have been actively studied and being put to practical use. The organic EL element is an element having a basic structure wherein a thin film of a hole injection material such as triphenyidiamine (TPD) is formed by vapor deposition on a transparent electrode (hole injection electrode, i.e. anode) such as tin-doped indium oxide (ITO), and further, a fluorescent substance such as aluminum-quinolinol complex (Alq3) is stacked as a light emitting layer, and further, a metal electrode (electron injection electrode, i.e. cathode) such as AgMg having a small work function is formed. Inasmuch as a very high luminance, i.e. several 100 to several 10000 cd/m2, can be obtained at an applied voltage of about 10V, attention has been paid thereto for household electrical appliances, electrical equipment of automobiles, bicycles, airplanes, etc., displays, and so on.
Such an organic EL element has a structure wherein, for example, an organic layer such as a light emitting layer is sandwiched between a scan (common line) electrode serving as an electron injection electrode, and a data (segment line) electrode serving as a hole injection electrode (transparent electrode), and formed on a transparent (glass) substrate. Those that are formed as displays are roughly divided into a matrix display that carries out dot display using scan electrodes and data electrodes arranged in a matrix, thereby to display information of an image, a character, or the like as an aggregate of those dots (pixels), and a segment display that displays those that independently exist as indicators having predetermined shapes and sizes.
In case of the segment display, it is also possible to adopt a static driving system that displays the respective indicators separately and independently. On the other hand, in case of the matrix display, a dynamic driving system is normally adopted wherein respective scan lines and data lines are driven in a time sharing manner.
Light emitters each forming a light emitting portion of an organic EL element are divided into a substrate surface light emitting type that uses a structure of a transparent substrate/a transparent electrode/a light emitting layer/a metal electrode wherein light generated in the light emitting layer is transmitted through the transparent electrode and the transparent substrate so as to be emitted, and a film surface light emitting type that uses a structure of a substrate/a metal electrode/a light emitting layer/a transparent electrode wherein light generated in the light emitting layer is transmitted through the transparent electrode so as to be emitted from the side of the film surface opposite to the side of the substrate surface.
The element of the substrate surface light emitting type is described in, for example, Applied Physical Letter, vol. 51, pp. 913-915 (1987) (Appl. Phys. Lett., 51, 913-915 (1987)).
The element of the film surface light emitting type is described in, for example, Applied Physical Letter, vol. 65, pp. 2636-2638 (1994) (Appl. Phys. Lett., 65, 2636-2638 (1994)).
However, in case of the foregoing substrate surface light emitting type, there has been raised a problem that since light is emitted from the side of the substrate surface, if an opaque substance such as a driving circuit or wiring is inserted between the substrate surface and the light emitting surface, light is blocked so that the aperture ratio and the luminance are lowered. Further, there has been a problem that since the metal electrode and the light emitting layer that are liable to be corroded are provided on the transparent electrode, unless sealing of the element is carried out without breaking vacuum after formation of the metal electrode, the light emitting property is degraded. The sealing technique for the light emitter is described in, for example, Laid-open Unexamined Patent Publication No. H8-124677.
On the other hand, in case of the foregoing film surface light emitting type, even if a driving circuit, wiring or the like is inserted between the substrate surface and the light emitting surface, the aperture ratio is not lowered. Further, the metal electrode and the light emitting layer that are liable to be corroded are located between the transparent electrode and the substrate. Therefore, by selecting sizes and a positional relationship of patterns of the metal electrode, the light emitting layer and the transparent electrode, the light emitting property is not immediately degraded even if vacuum is broken after film formation of the transparent electrode, so that it becomes possible to omit sealing of the light emitting element, and to form a protective layer after transfer into another film forming apparatus by once breaking vacuum after the formation of the transparent electrode.
The present invention has been made in view of the foregoing problems and has an object to provide a light emitter, a light emitting element, and a light emitting display device, which can provide a light emitting element structure than can ensure a long-term element light-emitting life duration with respect to a light emitting element of a film surface light-emitting type that can obtain a large aperture ratio, that can omit sealing of the light emitting element, and that can form a protective layer after transferring it to another film forming apparatus by breaking vacuum after formation of a transparent electrode.